Re: [PATCH] USB: ehci: use packed,aligned(4) instead of removing the packed attribute

[Nicolas Pitre]

On Mon, 20 Jun 2011, Russell King - ARM Linux wrote:

> On Mon, Jun 20, 2011 at 06:58:45PM +0200, Arnd Bergmann wrote:
> > We are also going to change the ARM implementation to always do 32 bit
> > accesses in readl/writel, but the patch that went into the ehci driver
> > was correct nonetheless.
> 
> Not without someone doing a comparitively large amount of work to analyze
> the effect of any change there and make sure that it doesn't have a
> negative impact to drivers.

This thread prompted me to investigate a bit.  I have vague memories for 
the reasons why we decided to use plain C for the IO accessors as the 
inline assembly version didn't produce nearly the same code quality.  It 
seems that GCC improved quite a bit there, and from a quick 
investigation, it looks like comparable code is being generated with the 
C and the inline asm versions with a recent enough GCC.  This is 
certainly the case with the version causing issues with packed 
structures.


Nicolas
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